Extended protein glues



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United States Patent 3,436,300 EXTENDED PROTEIN GLUES Fred Bryner, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Oct. 1, 1964, Ser. No. 400,942 Int. Cl. C09j 1/02 U.S. Cl. 161-210 Claims ABSTRACT OF THE DISCLOSURE Protein gl neg can be formulated into highly efiective adhesives "far -wEJod products, such as plywood, by the incorporation of a finely divided, water-insoluble p911- vale metaLcagbonatp in an amount from about 0.2 up 0 3 parts by weight, per part by weight of the protein glue base. Other ingredients of the complete formulation include from about 0.05 to about 0.3 part by weight of calcium hydroxide and from about 0.05 to about 0.35 pfifi'filwfil'gfit a. 11l$fl1i-mll.ilicate. Such extenders have been discovered to substantially improve the properties of casein glues.

The present invention relates broadly to the art of protein glues, particularly glues useful in the manufacture of plywood and other composite wood articles. More specifically, the invention concerns the preparation and use for this purpose of protein glues highly extended with finely divided, water-insoluble polyvalent metal carbonates.

Protein glues of both the animal and vegetable origin have long been used in the wood working industry and today occupy a market position of considerable significance, especially in the manufacture of interior grade plywood. Throughout their history of use, these glues have been variously modified to improve their strength properties, resistance to micro-organisms, and resistance to weathering effects.

It is an object of the present invention to provide a novel, thermosetting proteinaceous glue and more particularly it is an object to provide a glue having a high extension of the protein glue base and, thus, a lower cost. Particular objects are to provide a thermosetting protein glue useful for plywood manufacture having improved resistances to weathering and attack by micro'organisms. These objects, and other benefits which will become manifest hereinafter, are achieved in the present invention.

In one embodiment, the present invention is a liquid thermosetting proteinaceous glue comprising one part by weight of a proteinaceous glue base from about 0.05 to about 0.3 part by weight of calcium hydroxide, from about 0.05 to about 0.35 part by weight of alkali metal silicate and from about 0.2 up to 3 parts, preferably no more than about 2 parts, by weight of a finely divided, water-insoluble polyvalent metal carbonate and sufiicient water to provide a liquid composition. Optionally up to 0.15 part by weight of alkali metal hydroxide can be added as an additional catalyst to promote curing of the formulation, which may occur at ambient or elevated temperatures. For most applications, the glues will have total solids contents within the range from about 20 percent up to as much as 55 percent by weight of the total glue composition. Preferably the highly extended glue compositions of the invention contain from about 25 to about 45 percent by weight solids. In practice the amount of solids, or conversely water, utilized in the glue formulation will vary according to the dryness and type of the wood being glued, the particular type of proteinaceous material used as the glue base and, in the instance of plywood manufacture, the assembly time for the panels.

Such considerations affect both the amount of water required to achieve the desired glue fluidity for spreading and the amount of water in the glue line at the instant of application of thermosetting temperatures.

Proteinaceous glue base is in reference herein to proteins of animal and vegetable origin and mixtures thereof. The essential prerequisite is that the proteins be dispersible in and at least swollen by water. By vegetable protein is meant flours of such oleaginous seeds as soybean, peanut, cotton seed, linseed, sesame seed, castor oil bean, sunflower seed, safflower seed and the like. By animal protein is meant milk casein, soluble hide and bone glue, blood albumin, gelatin, fish glue, egg albumen and the like. The proteinaceous materials most often used in the preparation of glues are casein, soybean protein, and blood albumin.

For illustrations of prior protein glues containing a proteinaceous glue base, alkaline reagents as specified above, and water, refer to Delmonte, The Technology of Adhesives, Reinhold Pub. Corp., 1947, pp. 257-275.

The addition of the finely divided, water-insoluble polyvalent metal carbonate of the present invention converts the protein based glue to a superior adhesive for wood, especially wood plies in the manufacture of plywood.

As will be apparent from a consideration of the aforementioned reference, the proteinaceous material, alkaline reagents and water are the fundamentally essential ingredients for the portein glue to which any one of a nurnber of other additives may be added for special purposes. For instance, the glue may be modified to improve its strength properties and increase its water resistance. Also preservatives to prevent mold and fungi growth are conventional additives. In the present invention, however, the need for special additives to protect against attack by microorganisms is substantially, if not altogether, abated. Like the high extension, this factor also significantly reduces the cost of the glue formation.

Polyvalent metal carbonates satisfactory for use in the invention include the alkaline earth metal carbonates such as calcium carbonate and magnesium carbonate and in addition such other carbonates as manganese carbonate, cadmium carbonate, barium carbonate, nickel carbonate, zinc carbonate, lead carbonate and cupric carbonate. Minerals which are largely composed of insoluble, poly valent metal carbonates ,such as limestone, dolomite, magnesite, calcite, aragonite and the like are also useful.

In general, water-insoluble means herein that no more than about 0.5 gram of the carbonate dissolves in grams of water at 25 C. The terminology finely divided, as applied to the polyvalent metal carbonates, means these materials have an average particle size small enough to pass through an 80 mesh screen, preferably mesh screen of the Tyler mesh series.

To prepare the proteinaceous glue formulations of the invention, a substantial proportion of the proteinaceous glue base, preferably all of it, is dispersed in at least a major portion of the total water to be utilized in the formulation. To the resulting mixture is added in any order one or more of the necessary alkaline reagents along with an amount of the finely divided polyvalent metal carbonate to provide the desired extension of the protein solids. Alternately the metal carbonate is dry blended with the protein before dispersing it in water. Mixing is accomplished by any convenient means after each addition to the formulation.

A preferred formulation for utilization as a thermosetting plywood adhesive contains as glue solids one part by weight of casein, from about 0.05 to about 0.3 part by weight of calcium hydroxide, from about 0.05 to about 0.35 part by weight of sodium silicate. To this mixture is added from about 0.5 to about 2.0 parts by weight of finely divided CaCO Mixtures of the components of the desired formulation are stirred or otherwise blended with i i l l l i l water as required, preferably at room temperature, until a composition of uniform consistency or fluidity is obtained. The consistency of the glue formulation is controlled by adjusting the amount of water used within the aforementioned overall limits. Such a preferred formulation has substantially improved weathering and strength properties as compared to conventional thermosetting casin glues.

The adhesive formulations of the invention are spread on wood plies in amounts ranging from about 18 to about 30 pounds of total glue solids per thousand square feet of double glue line. The assembly time can vary from about 1 up to about 30 minutes, or more, but preferably from about to about 15 minutes. The press time for satisfactory results may range from about 2 to about minutes or more depending upon the temperature of the platens, the number of plies being bonded, the number of panels per opening and the like considerations affecting heat transfer, such as are apparent to those skilled in the art. After having been pressed and cured at the bonding temperature for the glue formulation, the plywood is removed from the press and stacked for conditioning.

The following examples illustrate various aspects of the invention and should not be construed as limitations thereof.

EXAMPLE 1 The present example illustrates the preparation of a highly extended proteinaceous glue in accordance with the invention and the improved weathering properties achieved thereby. Initially, however, a control adhesive was prepared according to the specifications of a commercial glue for the purposes of comparison. To 57 grams of water at about 55 F. was added 0.5 gram of pine oil and 30 grams of a soybean flour available under the trademark Casco W-1691 (Borden). The resulting mixture was stirred for 5 minutes after which 47.7 grams of water and 3.6 grams of calcium hydroxide were added with additional stirring for about 0.5 minute. At this point 3.6 grams of 50 percent aqueous caustic and 7.5 grams of 38 percent by weight sodium silicate were added, along with 0.5 gram of a water proofing mixture consisting of 75 percent by weight carbon disulfide and 25 percent by weight carbon tetrachloride. The formulation thus completed was mixed for an additional five minutes.

A second glue formulation was prepared in accordance with the invention by adding 60 grams of limestone fiour -to a formulation like that described above along with t p 17 grams of additional water to produce a liquid confeet of double glue line. The panels were given assembly times of 3 minutes after which they were hot pressed, one per opening at 110 C., under 200 pounds per square inch, for 2.5 minutes press time. Upon removal from the press, the panels were hot stacked at 95 C. for 2 hours.

Twenty-four hours later, 3 specimens 1% inches by 4 inches were cut from each panel and subjected to a cyclic immersion and drying test to determine the quality of the plywood thus prepared. Specifically the specimens were soaked in water at room temperature for a period of 4 hours and then removed and placed in an oven at a temperature of about 58 C. for 19 hours. This constituted one cycle which was repeated until the specimen failed. The specimens were considered as having failed when a total continuous delamination of inch, or more, iln depth occurred for at least 2 inches along any glue In the instance of the plywood prepared with the proteinaceous glue containing the limestone extender, 1 specimen failed in the 20th cycle while the 2 remaining specimens had not failed after 31 cycles. All specimens taken from the plywood panel prepared with the control protein glue of the prior art failed in the 18th cycle. Thus, not only was a less expensive glue made as the result of high extension with the limestone but also the properties of the glue as a thermosetting adhesive for wood were substantially improved.

EXAMPLE 2 The following operation illustrates the application of the invention to a dried blood plywood adhesive formulation. A control dry blood glue of commercial specifications was prepared by mixing 174 grams of water and 32 grams of soluble dry blood. To this mixture was added 0.4

gram of an antifoaming agent, 6.4 grams of 50 percent aqueous sodium hydroxide, 1.6 grams of calcium hydroxide and 10 grams of sodium silicate as a 38 percent by weight aqueous solution. Also added as a preservative was 1.4 grams of pentachlorophenol. With each of the mentioned additions, the resulting mixture was stirred for a period of time from 2 to 5 minutes until a uniform blend was obtained.

A highly extended protein glue of the invention was prepared in a manner similar to that of the foregoing, except that following the addition of the soluble dry blood to the water, 32 grams of limestone fiour and sufiicient additional water (about 12 grams) to produce a desirable consistency were added. The total additional mixing time was about 5 minutes. The extension of the protein solids with limestone fiour was percent.

The control and highly extended blood glues were utilized to prepare plywood test panels as in Example 1 except that panels were prepared with each glue using a 15 minute assembly time.

The panels were cut into 1 inch by 3 inches test specimens. The specimens from each panel were then subjected to a vacuum-pressure test in which they were immersed in water under a vacuum of 25 inches of water for 30 minutes and then subjected to a pressure of 60 p.s.i.g. for 30 minutes. Following this treatment, the specimens were sheared while wet. Wood failure was determined by visual inspection of the sheared specimens according to a standard technique. The percentage wood failure was determined for 4 test specimens from each panel and the range of this value is reported below.

TABLE 1 Panel No. Glue Percentage wood failure From the foregoing it is apparent that the highly extended and less expensive glue of the invention in this instance is just as good as the prior art glue as regards its bonding properties.

In a manner similar to that of the foregoing, other suitably finely divided, water-insoluble polyvalent metal carbonates such as dolomite fiour and magnesium carbonate can be substituted for the limestone flour utilized above to achieve comparable results with extensions ranging from 0.2 part up to as much as 3 parts of extender for each part of the proteinaceous material utilized in the formulation.

EXAMPLE 3 In a preferred embodiment of the invention, casein is the adhesive extended with a polyvalent metal carbonate. Not only is the casein made to go farther by the addition of the extender of the invention, but the strength properties of the combination have been found to be superior to those of the unextended casein formulation.

A control casein glue formulation was prepared accord ing to the specifications set forth in Delmonte, The Technology of Adhesives, Reinhold Pub. Corp. (1947), page 261.

Another batch of the above glue was modified in accordance with the invention by adding thereto an amount of limestone flour equal to the amount of casein in the formulation, i.e., 100 percent extension. Additional water was also added to give the formulation proper fluidity for convenient spreading on wood plies.

Each of the above casein glues were used to prepare plywood panels according to the procedure described in Example 1 except that panels were prepared at both 3 and minute assembly times.

The panels were cut into test specimens 1% inches by 4 inches. Two specimens from each panel were subjected to a cyclic cold soak test described in Example 1. For the panels prepared at 3 minute assembly times, the specimens glued with the control glue failed in the 16th and 20th cycles while those glued with the extended glue still had not failed after 23 cycles. For the panels prepared at 15 minute assembly times, the specimens glued with the control casein glue failed in the 2nd and 3rd cycles while of those bonded with the extended glue, one lasted until the 17th cycle and others still had not failed after 24 cycles.

This data demonstrates a most surprising superiority for the combination of casein and polyvalent metal carbonate in protein glues as compared to conventional casein glue with regard to weatherability of the glue line.

What is claimed is:

1. A liquid composition of matter comprising one part by weight of a casein glue base, from about 0.05 to about 0.3 part by weight of calcium hydroxide, from about 0.05 to about 0.35 part by weight of alkali metal silicate and from about 0.2 up to 2 parts by weight of a finely divided calcium carbonate and water in amount to provide a liquid mixture.

2. A liquid composition of matter comprising 1 part by weight of casein, from about 0.05 to about 0.3 part by weight of calcium hydroxide, from about 0.05 to about 0.35 part by weight of sodium silicate, from about 0.2 up to about 3 parts by weight of a finely divided calcium carbonate and water in amount sufiicient to provide a liquid mixture having a total solids content within the range from about 20 to about 55 percent by weight of the total composition.

3. An article of manufacture consisting of at least' 2 plies of wood bonded together with the thermal reaction product of the composition of claim 2.

4. A method for bonding plies of wood together which comprises applying to the surface of at least one of the plies a liquid glue comprising one part by Weight of a casein glue base, from about 0.05 to about 0.3 part by weight of calcium hydroxide, from about 0.05 to about 0.35 part by weight of alkali metal silicate, and from about 0.2 up to 3 parts by weight of a finely divided, water-insoluble polyvalent metal carbonate and water in an amount sufiicient to provide a liquid mixture, forming a laminate of the wood plies in mutual contact through the glue and applying heat and pressure to thermoset the glue.

5. A method as in claim 4 wherein the polyvalent metal carbonate used is calcium carbonate and the liquid mixture contains from about 20 to about percent by weight solids based on the weight of the total composition.

References Cited UNITED STATES PATENTS 1,976,435 10/ 1934 Cone 106-79 1,976,436 10/1934 Cone 106-79 2,044,466 6/ 1936 Cleveland et a1 106-79 2,330,428 9/1943 Hughes et al 106-148 2,354,318 7/1944 Hughes et a1 106-148 3,095,571 6/1963 Cone 106-79 3,206,320 9/1965 Davidson 106-161 3,206,321 9/1965 Davidson 106-161 3,274,042 9/1966 Gilboe et a1. 106-154 3,301,692 1/1967 Karjala et a1 106-161 3,323,928 6/1967 Weisfeld 106-148 FOREIGN PATENTS 468,329 7/ 1937 Great Britain.

TOBIAS EJLEVOW, Primary Examiner.

S. E. MO'IT, Assistant Examiner.

US. Cl. X.R. 

